The present invention relates to an automatic warehouse system for information data storage devices or units such as magnetic tapes and optical disks and more particularly to an information storage control system for such storage devices or units.
There are systems that automatically install transportable data storage units such as magnetic tapes and optical disks into a read/write apparatus for reading and writing data to and from the data storage units. Among them, there is known an automatic warehouse system for storage devices (hereinafter referred to as a data storage unit library system).
The magnetic tape library system has a storage shelf or holder to store several thousand to tens of thousands of data storage units. In response to a mount request from a higher-level system, a robot or handler picks up a certain data storage unit from the shelf, and transports and mounts the data storage unit to and on the read/write apparatus. Upon receiving a demount request from the higher-level system, the handler takes the data storage unit out of the read/write apparatus, and transports it to and puts it on the storage shelf.
The magnetic tape library system spends a greater amount of time before a file can become available for use than is taken by a direct access storage device represented by a magnetic disk device. This is because the magnetic tape library system requires a picking time for the handler to become available for picking up from the shelf the data storage unit in which a desired file is recorded, a carry time for the handler to carry the data storage unit to the read/write apparatus, a mount time for the data storage unit to be mounted on the read/write apparatus, and an access time for the read/write head to be positioned at the file. For this reason, the magnetic tape library system is used mainly as a storage equipment for file backup and data archival storage, rather than as an on-line storage equipment.
In such a magnetic tape library system, a mount/demount method is known which determines a data storage unit that is likely to be used in the future according to such information as a past utilization record of the storage devices and a job execution schedule, and then mounts it on the read/write apparatus to reduce the time taken by the mounting and demounting of the storage device, thus improving the efficiency of data storage unit mounting and demounting. One such method is described, for example, in Japanese Patent Laid-Open No. 205649/1991, which corresponds to U.S. application Ser. No. 07/591,233 now U.S. Pat. No. 5,353,422.